iOS (jailbreak): Orbit is a handy jailbreak hack that adds home screen page switching in the style of Mac OS X's Expose feature. This is very useful if you've got a lot of apps and pages to manage.
Orbit's functionality is very simple. After you purchase it from Cydia ($US2) and install it, you just have to assign it a gesture using Activator -- another jailbreak hack that will be installed alongside it (unless you already have Activator installed). As you can see in the video above, I assigned a single home button press on the home screen. This seems to be the most logical option, but you can use whatever you prefer.
If you want to give it a shot, be sure to download the correct version. Currently there are two versions of Orbit -- one for iOS 3.x and one for iOS 4 and higher. If you purchase the wrong version you should be able to download the other without issue and Cydia should bar you from installing if it won't work on your device. If you accidentally get the wrong one, you should be able to resolve that with a quick search on Cydia.
Download Orbit by searching for "Orbit" in Cydia.